1. Field of the Invention
The present invention relates to a method of mounting electronic components and a component mounting apparatus implementing the method More particularly, the present invention relates to a method of mounting electronic components wherein electronic components such as, for example, an integrated circuit, a diode, a condenser, or a resistor are automatically mounted. The present invention also relates to a component mounting apparatus implementing the method.
2. Description of the Related Art
Component mounting apparatuses are the most important of component mounting and assembling apparatuses for mounting components to a printed circuit board (PCB). They receive various kinds of electronic components from a component supply apparatus, transfer them to a mounting position of the PCB, and mount them to the PCB.
In general, component mounting apparatuses comprise a bed and X and Y axis movement mechanisms for guiding the PCB to a predetermined position, a component supply unit for supporting various kinds of electronic components to be mounted to the PCB, and a head unit for absorbing or detaching the components. The head unit is vertically moved in order to mount the electronic components supported by the component supply unit to the PCB and
Recently, a plurality of nozzle spindles have been provided to component mounters. The nozzle spindles have been arranged in a line in a head assembly in order to absorb, either serially or in parallel, a plurality of electronic components, parallelly move the absorbed plurality of electronic components to a conveyor, and mount to the PCB, either serially or in parallel, the electronic components moved to the conveyor, thus increasing the efficiency of mounting components.
However, in these component mounters, the size of nozzle spindles provided to the component mounter in a line increases with their number, whereby the whole size of the head assembly increases. Therefore, the number of nozzle spindles provided in the head assembly should be limited.
As disclosed in Japan Unexamined Patent Application Publication No. 2003-273582, in order to solve such a problem, three revolver-type head assemblies 11 are arranged in a line at a head unit 10 provided to the component mounting apparatus, as shown in FIG. 1 and FIG. 2. Each nozzle spindle 40 provided in each head assembly 11 is arranged apart from each other along the same circumference from a center of a spline shaft 35 (see FIG. 2) and a nozzle 42 is coupled to the lower side of each nozzle spindle 40. These head assemblies 11 are fixed to a head frame 12.
The nozzle spindles 40 provided in each head assembly 11 are selected to descend by a nozzle selection mechanism 70 and descended by a nozzle lift mechanism 80. Further, each nozzle spindle 40 is rotated by a nozzle rotation mechanism 60. That is, the nozzle spindles 40 coupled to a spline shaft 35 are rotated because the spline shaft 35 is rotated by the nozzle rotation mechanism 60,
The head assembly 11 provided in the component mounting apparatus having such a structure will be described in detail with reference to FIG. 2. One head assembly 11 is provided with a plurality of nozzle spindles 40 installed along the same circumference about the spline shaft 35.
The nozzle holder 50 is coupled to the spline shaft 35, and the nozzle spindles 40 are arranged along the same circumference about the spline shaft 35 of the nozzle holder 50 and are able to be vertically moved.
The nozzle spindles 40 are provided to allow them to ascend or descend. The spline shaft 35 is rotated by driving the nozzle rotation mechanism 60 that comprises a motor for rotating nozzles, whereby the nozzle spindles 40 and the nozzle holder 50 coupled to the spline shaft 35 are rotated.
A nozzle selection mechanism 70 and a nozzle lift mechanism 80 are provided in the head assembly 11 to separately select the nozzle spindles 40 to descend. The nozzle selection mechanism 70 comprises a compressed air supply unit 71 and a nozzle selection valve 72 and injects compressed air into a pressurized air supply unit 32 corresponding to the nozzle spindles 40 selected to descend. In this case, the pressurized air supply unit 32 is coupled to the head assembly 11, is a space inside an air cylinder block 30 arranged at an upper side of the nozzle holder 50, and is connected to each nozzle spindle 40.
Therefore, a piston 52 formed within the pressurized supply unit and an air cylinder shaft 53 coupled to a lower side of the piston descend when air of a positive pressure is injected into the pressurized air supply unit arranged at an upper side of the nozzle spindles 40 selected to descend. Thereby, a lower end 53a of the air cylinder shaft 53, an upper end 40a of the nozzle spindles coupled to the lower end 53a of the air cylinder shaft 53, and an upper surface 85a of operation of a spline nut 85 are the same height, making the air cylinder shaft 53, the nozzle spindles 40, and the spline nut 85 become one piece. The spline nut 85 is coupled to the nozzle lift mechanism 80 having a cam follower 84, an eccentric cam 82, and a drive motor 81 and is vertically translated, whereby the nozzle spindles 40 coupled to the spline nut 85 descend.
The vacuum absorption mechanism 90 is provided to absorb electronic components. The vacuum absorption mechanism 90 provides the nozzle spindles 40 with air of a negative pressure from outside and air of a negative pressure from a negative-pressure air supply unit 91 individually, by means of absorption valves 92 provided on the outside of the nozzle holder 40, so that the nozzle spindles 40 individually absorb electronic components. The revolver type of head unit has a small size but can mount many electronic components.
A conventional head assembly 11 for mounting components having such a structure is provided with the nozzle lift mechanism 80 to descend the nozzle spindles 40. The nozzle lift mechanism 80 comprises an eccentric cam 82, a cam follower 84, and a spline nut 85. Thus, its lift mechanism becomes complicated, its weight is heavy, and it occupies much space. Therefore, it is difficult for the nozzle lift mechanism to cope with various work environments and to modularize the head assembly.
Further, in a conventional component mounting apparatus, a positional difference occurs when the conveyor is not accurately placed during assembly or when the PCB is not placed parallel to the conveyor when the PCB is positioned. However, in the component mounting apparatus disclosed in Japan Unexamined Patent Application Publication No. 2003-371456, the nozzle spindles 40 rotate as the spline shaft 35 rotates, so that it is possible to compensate for a difference in a specified mounting position on the electronic components or the PCB.
However, when mounting the electronic components on the PCB, the electronic components mounted to the lower side of the nozzle spindles 40 are also rotated when rotating the nozzle spindles 40 in order to compensate for the difference, whereby the electronic components rotate to a certain angle from a specified mounting position of the PCB and are therefore not put in a right position.
Such a problem also occurs in a case where two or more head units are provided to the component mounting apparatus. That is, in a case where a Y axis position of one head unit is the same as that of the PCB corresponding to the Y axis position of one head unit in order to composite for the difference, a Y axis position of the other head unit is not the same as that of the PCB corresponding to the Y axis position of the other head unit. Thereby, it is impossible to mount electronic components to the PCB because nozzles in two or more head units “provided to the component mounting apparatus” descend at the same time.